The Asynchronous Transfer Mode (ATM) method of transmitting and switching multimedia information is replacing older circuit and packet switching techniques, allowing flexible, fast and cost effective provision of new telecommunications service. Among these services are Internet access, Basic rate ISDN, fractional T1/E1 support of cellular PCN network and LAN traffic routing.
These services require expensive infrastructure of transmission facilities, such as copper lines, fiber optics, cable TV or hybrid fiber-coax (HFC). In a competitive environment in which some new telecommunication service providers own some or none of the above facilities, wireless is the other alternative for timely and cost effective deployment of transmission networks. Two previous patent applications (application Ser. No. 08/388,110 filed Feb. 13, 1995 now U.S. Pat. No. 5,648,969 and application Ser. No. 08/538,327 filed Oct. 3, 1995 now U.S. Pat. No. 5,710,756 both assigned to the same assignee and both incorporated herein by reference in their entirety) disclose the structure of reliable networks based on point-to-point radio links. These links allow reliable transmission of ATM traffic with minimum link errors and ATM cell misinsertion. These links are cost effective for high bandwidth and continuous transmission. However, these systems make bad use of equipment and spectrum for applications of intermittent nature such as telephone calls over a wireless link. When a telephone is on hook, the spectrum should be freed for other potential users, and so should the central office transceiver that served that telephone. Data traffic does not always follow the behavior of voice calls. Data may flow slowly, requiring low baud rate for transmission, followed suddenly by a burst of high speed traffic. For efficient use of spectrum, it is desired to allocate bandwidth on demand in a fast and efficient way to handle such bursty information.
These requirements can be served by a multiple access network that uses ATM cells to emulate the variety of services, and by the use of a media access control (MAC) protocol to arbitrate the transfer of data over the air.
ATM services include Constant Bit Rate (CBR), suitable for telephony and video, Variable Bit Rate (VBR), suitable for video applications with variable compression, Available Bit Rate (ABR) suitable for data transactions, and Unspecified Bit Rate (UBR), suitable for e-mail or other non-delay sensitive applications. A MAC layer must support efficiently all of these services.
Due to the high bandwidth required for serving many customers with varying bit rate requirements, high total bandwidth is required in such links. This bandwidth is available only at high microwave frequencies, usually in the range of 10--40 GHz.
The economy of point-to-multipoint systems favors delegating as many functions as possible to the base station ("point") serving the subscriber terminals ("multi-point"), thus saving the cost of replicating the same function in all terminals.
There is, therefore, a need for a point-to-multipoint wireless metropolitan area network with MAC layer suitable for a variety of ATM services, operating at microwave frequencies and allowing cost-effective subscriber radio terminals.